This Mentored Research Scientist Development Award (K01) will enable me to 1) acquire expertise in the research methods of developing structural HIV prevention interventions targeting substance using female sex workers (FSWs); 2) increase knowledge of substance abuse epidemiology, assessment and prevention; 3) obtain additional training in the culturally competent ethical conduct of research involving behavioral and biological HIV/STI data collection, violence measurement, and structural interventions in a new international setting; 4) learn how to design RCTs of interventions and conduct related longitudinal data analyses (GLMM); 5) hone skills needed for a successful academic career studying the intersection of substance use, HIV/STI acquisition, and structural risk and protective factors among high risk populations, including grantsmanship and disseminating scientific research findings nationally and internationally. My career development plan will include a mixture of didactic courses, seminars, hands-on field research experience, and mentored independent studies which will provide me with training in intervention evaluation methodologies, substance use epidemiology, and clinical biomarkers. For example, I will take courses in longitudinal data analyses (e.g. event history and survival, and cost-benefit analyses). I will work with a world-renowned mentoring team and an infrastructure already in place in Mexico, with the goal of applying what I learn to other national contexts as well. I will train in intervention adaptation while simultaneously practicing rigorous RCT evaluation methodologies (Generalized Linear Mixed Modeling (GLMM)) on existing data, with the goal of becoming one of a few structural HIV prevention intervention researchers for FSWs worldwide. My proposed K01 project Mujeres Unidas (Women United) will be embedded in the NIDA funded parent grant, Proyecto Mapa de Salud (R01DA028692-01, PI: Brouwer), which explores HIV/STI transmission among FSWs and other vulnerable populations along the Mexico/U.S. border. In Tijuana, Mexico, Mujeres Unidas will 1) qualitatively interview FSWs (N=30) and FSW advocates/organizers (N=20) about community mobilization and the role of substance use; 2) adapt measures of community mobilization to the Tijuana context through cognitive testing with FSWs (n=10) to ensure readability and acceptability, and 3) determine the prevalence of community mobilization participation and its association with substance use, HIV/STI prevalence and sexual risk behaviors among FSWs by adding adapted measures to the parent grant's 12- month follow up surveys (N=300 FSWs). Results will generate pilot data for a future R34 grant application to pilot/feasibility test an adapted preventive intervention targeting drug use and HIV infection acquisition.